Pfthb

I am fighting with an internal caching (about 90 MB for 15 mp image ) in CGContextDrawImage/CGDataProviderCopyData functions.

Here is the stack-trace in profiler:

In all cases, IOSurface is created as a "cache", and isn't cleaned after @autoreleasepool is drained.
This leaves a very few chances for an app to survive.

Caching doesn't depend on image size: I tried to render 512x512, as well as 4500x512 and 4500x2500 (full-size) image chunks.

I use @autoreleasepool, CFGetRetainCount returns 1 for all CG-objects before cleaning them.

The code which manipulates the data:

+ (void)render11:(CIImage*)ciImage fromRect:(CGRect)roi toBitmap:(unsigned char*)bitmap 
 @autoreleasepool
 
 int w = CGRectGetWidth(roi), h = CGRectGetHeight(roi);

 CIContext* ciContext = [CIContext contextWithOptions:nil];
 CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

 CGContextRef cgContext = CGBitmapContextCreate(bitmap, w, h,
 8, w*4, colorSpace,
 kCGImageAlphaPremultipliedLast 

What I know about IOSurface: it's from the previously private framework IOSurface.
CIContext has a function render: ... toIOSurface:.

I've created my IOSurfaceRef and passed it to this function, and the internal implementation still creates its own surface, and doesn't clean it.

So, do you know (or assume):

1. Are there other ways to read CGImage's data buffer except
CGContextDrawImage/CGDataProviderCopyData ?

2. Is there a way to disable caching at render?

3. Why does the caching happen?

4. Can I use some lower-level (while non-private) API to manually clean up system memory?

Any suggestions are welcome.

If you just need to manipulate CIImage data, may consider to use CIImageProcessorKernel to put data into CPU or GPU calculation without extracting them.

I notice that

[ciContext
render:image toBitmap:bitmap rowBytes: w*4 bounds:image.extent format:kCIFormatRGBA8 colorSpace:colorSpace];

There is no such 90M cache. Maybe it's what you want.